I've been using a cheap electronic metronome to practice my scales. It sounds like beep beep beep BOOP, beep beep beep BOOP, which was getting pretty annoying so I decided to look online to see if I could find something that I can customize the tones. I came across this:
I also found this great Online Drum Machine if you want a custom beat to accompany chords or scales.
I'd like to find an online metronome where the tempo increases at whatever intervals you want. For example, you could set it to increase by 2 or 5 units of tempo every 4 notes. It would help me build up speeds in increments. I'll keep looking.